Dianhydrohexitol diester mixture GC

ABSTRACT

An ester mixture of dianhydrohexitol, a composition comprising the ester mixture and a polymer composition comprising the ester mixture or the composition, the use thereof, and a process by which the ester mixture can be prepared, where the proportion of C8 based on the sum of C8 and C10 in the overall ester mixture is 45 mol % to 85 mol %.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of PCT/EP2012/076064, which wasfiled on Dec. 19, 2012. This application is based upon and claims thebenefit of priority to German Application No. 10 2011 089 495.0, whichwas filed on Dec. 21, 2011.

The present invention concerns an ester mixture of dianhydrohexitol, acomposition comprising the ester mixture and a polymer compositioncomprising the ester mixture or the composition, the use thereof, andalso a method whereby the ester mixture is obtainable.

The polymer composition may comprise for example polyvinyl chloride(PVC), polylactic acid (PLA), polyurethane or polyhydroxyalkanoates.

Polyvinyl chloride (PVC) is commercially one of the most importantpolymers. It is widely used both as rigid PVC and as flexible PVC.

Flexible PVC is produced by additizing the PVC with plasticizers,predominantly phthalic esters, in particular di-2-ethylhexyl phthalate(DEHP), diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP).Existing and possibly future legislation regulating the usage ofphthalates has created a need to find novel esters useful asplasticizers for PVC and other polymers.

U.S. Pat. No. 2,387,842 describes isomannide dibutyrate, isosorbidedi(acetate/butyrate), isosorbide dihexanoate, isosorbide dioctanoate andisosorbide di-2-ethylhexanoate as useful PVC plasticizers. Thecorresponding flexible PVC test specimens were produced by use ofsolvents, i.e. under less than ideal industrial conditions. Preferredisosorbide esters were those obtained from mixtures of carboxylic acids.There should be 2 to 9 carbon atoms in the first carboxylic acid and 3to 10 carbon atoms in the second one subject to the proviso that the sumof the carbon atoms should be at least 5 and not greater than 18.

WO 99/45060 describes inter alia C3-C11 alkanoates of isosorbide or ofisomannide. Examples describe the synthesis of an isosorbide dioctanoate(IsDO) and also of the isosorbide esters based on butyric acid (IsDB),hexanoic acid (IsDH) and 2-ethylhexanoic acid (IsDEH) and report someperformance characteristics in plasticized polymers (PVC andnitrocellulose).

WO 2001/083488 describes a method of producing anhydroglycitol esters,for example isosorbide esters, having improved colour, and postulateshigh conversions (98-100%) by using macroporous acidic ion exchangers asesterification catalyst. Corresponding diesters based on C3-C20carboxylic acids were said to be advantageous for the process. Estersbased on C6-C12 carboxylic acids were referred to as suitable for use asplasticizers. The synthesis of isosorbide di-n-octanoate (IsDO) andisosorbide di-2-ethylhexanoate (IsDEH) was exemplified.

WO2006/103338 describes a method of producing inter alia isosorbideesters by using a combination of two catalysts, one of which ishypophosphorous acid. This appears to give esters having better colournumbers and higher purities than described in WO2001/083488 for example.Again, only 2-ethylhexanoic acid and n-octanoic acid were explicitlyreferred to as carboxylic acids which can be reacted using this method.

WO 2008/095571 describes synthesis and use of mixtures of isosorbideesters obtainable by esterifying isomeric nonanoic acids (branched andlinear) with isosorbide. However, plastisols based on this plasticizerhave a significantly higher viscosity than that of the current standardplasticizer diisononyl phthalate (DINP), portending worseprocessability. Similarly, the glass transition temperatures are verysignificantly inferior to that of DINP.

The melting point of the pure isosorbide diester of n-octanoic acid isonly just below room temperature, so using the ester at lowertemperatures would be uncommercial in many processing methods of PVCplastisol technology.

The corresponding pure isosorbide di-n-decanoate even has a meltingpoint above 35° C., and is largely incompatible with PVC.

The problem addressed by the present invention was that of finding adianhydrohexitol-based diester or diester mixture having improvedperformance characteristics.

The problem is solved by an ester mixture as defined in Claim 1.

An ester mixture comprising a compound conforming to formula I:

wherein R¹ and R² are each independently selected from: C8-alkyl linear,C8-alkyl branched, C8-alkene wherein said C8-alkene may be partially orcompletely epoxidized, C10-alkyl linear, C10-alkyl branched, C10-alkenewherein said C10-alkene may be partially or completely epoxidized, and

wherein the carbon atom which binds the particular R¹ or R² moietydirectly to the oxygen in formula I is linked via a double bond to afurther oxygen atom, and

wherein the proportion of C8 based on the sum of C8 and C10 in theentire ester mixture is in the range from 45 mol % to 85 mol %.

C8 or as the case may be C10 refers to the number of carbon atoms in thecarbon chain.

The proportion of C10 in the ester mixture computes as the sum of C8 andC10 in the ester mixture (corresponds to 100 mol %) minus the proportionof C8.

For example, a mixture consisting to equal parts of pure C8-diester andpure C10-diester has a 50 mol % proportion of C8. But, for example, apure C8/C10-ester, i.e. an ester wherein one alcohol group is esterifiedwith C8 and the other alcohol group is esterified with C10, similarlyalso has a 50 mol % proportion of C8. The latter is also an estermixture for the purposes of this invention.

“In the entire ester mixture” is to be understood as also comprehendingthose esters in the ester mixture which do not conform to formula I, forexample monoesters of dianhydrohexitol which are present in the estermixture. Following saponification of the entire ester mixture, all theC8-acids and all the C10-acids are captured separately and ratioed.

The C8/C10 ratio is captured via gas-chromatography analyses of themethyl esters of the corresponding fatty acids.

The number of different esters in the ester mixture is preferably atleast two and more preferably at least three.

The ester mixture preferably comprises at least two esters that differin their total number of carbon atoms. That is, for example, aC8,C8-ester and a C8,C10-ester.

In a further embodiment, the proportion of C8 based on the sum of C8 andC10 in the entire ester mixture is in the range from 45 mol % to 75 mol%.

In a further embodiment, the proportion of C8 based on the sum of C8 andC10 in the entire ester mixture is in the range from 45 mol % to 65 mol%.

In a further embodiment, the proportion of C8 based on the sum of C8 andC10 in the entire ester mixture is in the range from 50 mol % to 65 mol%.

In a further embodiment, the sum of C8 and C10 has a proportion of above50 mol % in the entire ester mixture based on all acid chains.

If the entire ester mixture is transesterified and the methyl estersresulting therefrom are all captured analytically, then the C8-acids andC10-acids together comprise an above 50 mol % proportion of the mixtureof all acids.

The sum of C8 and C10 preferably has a proportion of above 60 mol % inthe entire ester mixture based on all acid chains, more preferably above70 mol % and most preferably above 80 mol %.

Formula I and its stereocentres preferably have the spatial structure ofisosorbide.

In one embodiment, the doubly esterified alcohol is isosorbide.

In one embodiment, R¹ is selected from: C8-alkyl linear, C10-alkyllinear.

In a further embodiment, R² is selected from: C8-alkyl linear, C10-alkyllinear.

In a further embodiment, the ester mixture comprises a mixture of thefollowing three compounds:

A composition comprising the ester mixture is claimed as well as theester mixture.

The composition comprises one of the ester mixtures described above, ahigh boiler and/or a low boiler.

The composition may also include two or more high boilers, i.e. ahigh-boiler mixture, and also two or more low boilers, i.e. a low-boilermixture.

High boiler in connection with this invention is to be understood asmeaning a compound with a boiling point above that of the C10,C10-ester.For example, high boilers have a higher retention time on an apolarcolumn than the C10,C10-ester in a gas-chromatographic analysis of thecomposition.

High boilers can arise for example as a result of correspondingfractions of other carboxylic acids, for example C12 or C14, beingpresent in the carboxylic acid mixture used for the reaction andC10,C12-esters or C10,C14-esters for example being formed as aconsequence. High boilers can further be formed by partial ring-openingof the feed dianhydrohexitol to the monoanhydrohexitol with subsequentesterification to the corresponding di-, tri- or tetraesters ofmonoanhydrohexitol with the corresponding carboxylic acids.

Low boiler in connection with this invention is to be understood asmeaning a compound with a boiling point below that of the C8,C8-ester.

For example, low boilers have a lower retention time on an apolar columnthan the C8,C8-ester in a gas-chromatographic analysis of thecomposition.

Low boilers can be the result for example of corresponding fractions ofother, generally shorter-chain, carboxylic acids such as, for example,C6 or C4 being present in the carboxylic acid mixture used for thereaction and C6-C8-esters or C4-C8-esters for example also being formedas a consequence.

Low boilers can also be formed as a result of incompletely convertedisosorbide esters (monoesters) remaining in the product or being formedfor example by partial hydrolysis during the work-up after the reaction.

Technical-grade mixtures of fatty acids may contain for example not onlyshorter-chain but also longer-chain carboxylic acids, as is the case forexample with so-called forerun fatty acids which are obtainable frompalm kernel oil or coconut oil and are commercially available as EdenorV85 (from Emery) or C-810L (P&G Chemicals) for example.

In a further embodiment, the proportion of high boilers is less than 15area % based on the ester signals of the composition.

In a further embodiment, the proportion of high boilers is less than 5area % based on the ester signals of the composition.

In a further embodiment, the proportion of high boilers is less than 2.5area % based on the ester signals of the composition.

A lower proportion of high boilers improves certain performancecharacteristics.

In a further embodiment, the proportion of low boilers is less than 4.5area % based on the ester signals of the composition.

In a further embodiment, the proportion of low boilers is less than 2.5area % based on the ester signals of the composition.

In a further embodiment, the proportion of low boilers is less than 1area % based on the ester signals of the composition.

The area % proportions are determined using merely ester signals, i.e.low boilers and high boilers as per the above definition and the diestermixture itself; that is, solvent or carboxylic acid signals are notco-integrated.

A lower proportion of high boilers improves certain performancecharacteristics.

A further claim is to a polymer composition comprising one of the estermixtures described above or one of the compositions described above.This polymer composition, in addition to the ester mixtures of thepresent invention, may also comprise one or more other plasticizers.

In one embodiment, the polymer composition comprises one of the estermixtures described above and also a polymer.

The polymer preferably comprises polyvinyl chloride (PVC), polylacticacid (PLA), polyurethane or polyhydroxyalkanoates, more preferably PVC.

In a further embodiment, the polymer composition comprises one of thecompositions described above and also a polymer.

The polymer preferably comprises polyvinyl chloride (PVC), polylacticacid (PLA), polyurethane or polyhydroxyalkanoates, more preferably PVC.

In addition to the ester mixture itself, the use thereof as aplasticizer is also claimed. Preferably as a plasticizer for a polymer,more preferably as a plasticizer for polyvinyl chloride (PVC).

The use of the composition as a plasticizer is also claimed. Preferablyas a plasticizer for a polymer, more preferably as a plasticizer forpolyvinyl chloride (PVC).

A further problem addressed was that of providing a method whereby adianhydrohexitol-based diester or diester mixture having improvedperformance characteristics is obtainable.

This problem is solved by a method as defined in claim 13.

A method comprising the steps of

-   -   a) providing a dianhydrohexitol,    -   b) admixing n-octanoic acid and n-decanoic acid,    -   c) esterifying the acids of b) with the alcohol of a) in the        presence of at least one catalyst,    -   d) terminating the esterifying reaction of c) as soon as the        proportion of monoester has fallen below 2.0 area %.

It was surprisingly found that controlling the proportion of monoestersin the reaction mixture provides control over not only the proportion oflow boilers but also the proportion of high boilers in the productmixture.

The proportion of monoesters which are low boilers rises significantlyat the start of the reaction. The monoesters formed then react to formthe diesters. At times the gas-chromatographically determined fractionof monoesters exceeds 25 area %.

The terminating in step d) is thus effected after the fraction ofmonoesters has first risen to beyond 2.0 area % and then, due to thefurther conversion to the diester in the later course of the reaction,there is a drop in the monoester fraction to below 2.0 area %.

The content level of low and high boilers can be determined by gaschromatography for example. In gas chromatography, high boilers have ahigher retention time on an apolar column than the C10,C10-ester. Lowboilers have a lower retention time on an apolar column than theC8,C8-ester. According to the present invention, the signals in the gaschromatogram are assigned using GC/MS analyses.

The area % proportions are determined using merely ester signals, i.e.low boilers and high boilers as per the above definition and the diestermixture itself; that is, solvent or carboxylic acid signals are notco-integrated.

Control over the product composition is achieved by terminating thereaction as the monoester content decreases to below a limiting value.This terminating the reaction is to be understood as meaning that thereaction mass is cooled down by more than 20 K from the previous settingof the reaction temperature. This cooling down can take the form ofactively cooling or else be passive in that the heating element isswitched off and no further heat is supplied.

This method is useful, for example, for obtaining the ester mixturesdescribed above.

In one embodiment of the method, the dianhydrohexitol provided in stepa) comprises isosorbide.

In one embodiment of the method, the terminating in step d) is effectedas soon as the proportion of monoester has dropped below 1.6 area %.

This can be used to maintain the proportion of low boilers at a lowvalue.

In one embodiment of the method, the terminating in step d) is effectedas soon as the proportion of monoester has dropped below 1.0 area %.

This can be used to maintain the proportion of low boilers at aparticularly low value.

In one embodiment of the method, the catalyst used in step c) ishypophosphorous acid.

This provides particularly good conversions, selectivities and colournumbers.

In a further embodiment, step c) utilizes a catalyst mixture which, inaddition to hypophosphorous acid, may additionally also comprise acidicion exchangers, sulfuric acid, toluenesulfonic acid, methanesulfonicacid or metal-containing catalysts such as, for example, tetraalkyltitanates.

In one embodiment of the method, the carboxylic acids in step b)comprise n-octanoic acid and n-decanoic acid.

The ester mixtures obtained by using these carboxylic acids haveparticularly good performance characteristics.

In one embodiment of the method, n-octanoic acid and n-decanoic acid areadmixed in step b) in a molar ratio in the range from 85:15 and 45:55.

Using the carboxylic acids in this ratio provides ester mixtures havingparticularly good performance characteristics.

In one embodiment of the method, n-octanoic acid and n-decanoic acid areadmixed in step b) in a molar ratio in the range from 80:20 and 45:55.

Using the carboxylic acids in this ratio provides ester mixtures havingparticularly good performance characteristics.

The ester mixtures obtainable by one of the methods described above areclaimed as well as the method.

The ester mixtures obtained according to one of the methods describedabove are further claimed.

The use as plasticizers of the ester mixtures obtained or obtainable bythis method is also claimed.

The invention will now be more particularly elucidated with workingexamples.

Preparing the Ester Mixture:

The method used can be used to esterify a dianhydrohexitol or a productcomprising at least 95% by weight of dianhydrohexitol with thecorresponding carboxylic acids in the presence or absence of a catalyst,preferably in the presence of hypophosphorous acid. The carboxylic acidsor carboxylic acid mixture used to form the ester are preferably used inexcess, preferably at a molar excess of 5 to 50 mol %, in particular 10to 30 mol %, of the molar amount needed to form the diester.

The dianhydrohexitol compound used as starting material can be inparticular an isosorbide. The isosorbide may comprise solid isosorbideor aqueous solutions of isosorbide.

To remove the water of reaction formed in the course of theesterification, the water of reaction can advantageously be distilledout of the reaction mixture together with the carboxylic acid(s). Thecarboxylic acid(s) thus serve as entrainer.

A possible method of esterification is described for example inWO2006/103338.

The comparative sample ISDIN-IS (to prepare recipe 2 in Table 2) wasobtained as described in Examples 1 and 2 of WO2008/095571.

Ester mixtures 3 to 10, as discussed hereinbelow (cf. Table 1), wereobtained as follows:

1.2 mol of isosorbide (from Cerestar), 2.8 mol of a defined C8/C10 fattyacid mixture (each from Sigma Aldrich) having a composition as per Table1 and 0.015 mol of hypophosphorous acid (50% aqueous solution, fromSigma Aldrich) were initially charged to an esterification apparatusconsisting of a 1 l multi-neck flask equipped with a stirrer, animmersion tube, a sampling stud, a thermometer and a water separatormounted with an intensive condenser (batches 3 to 10).

The apparatus was flushed with 6 l of N₂/hour per hour via the immersiontube before the start of the reaction. The reaction itself took placewith nitrogen sparging. The reaction mixture was graduallytemperature-regulated to 240° C. with stirring. A temperature of about200° C. marked the onset of boiling. By-produced water at the onset ofboiling was continuously removed from the reaction via the waterseparator. The esterification generated about 43 ml (2.4 mol) of waterof reaction. The reaction time was about 4.5 hours.

The reaction was tracked by gas chromatography. The batch wasdiscontinued as soon as the proportion of monoester had dropped below2.0 area %.

For aftertreatment, the reaction effluent from the esterification wastransferred into a 1 l flask which, following admixture of 2% by weightof activated carbon (CAP Super from Norit), was connected to a Claisenbridge with vacuum divider. An immersion tube with nitrogen terminus anda thermometer were fitted. Then, starting at 210° C. in vacuo (<40mbar), the bulk of the excess acid was distilled off while the remainingacid was subsequently removed by stripping with nitrogen at 190 to 200°C. (in the course of about 2 hours). The reaction mass was subsequentlycooled down to <90° C. and the flask was vented with nitrogen. The esterwas filtered through a Büchner funnel with filter paper and precompactedfilter cake of filter aid (D14 Perlite) via a suction bottle. Thefiltrate was subjected to a GC analysis.

Product 11 (cf. Table 1) was synthesized according to the followingprotocol:

2.5 mol of isosorbide (from Cerestar), 6.0 mol of a defined C8/C10 fattyacid mixture (each from Sigma Aldrich) as per number 11 in Table 1 and0.034 mol of hypophosphorous acid (50% aqueous solution, from SigmaAldrich) were initially charged to an esterification apparatusconsisting of a 4 l multi-neck flask equipped with a stirrer, animmersion tube, a sampling stud, a thermometer and a water separatormounted with an intensive condenser.

The apparatus was flushed with 6 l of N₂/hour per hour via the immersiontube before the start of the reaction. The reaction itself took placewith nitrogen sparging. The reaction mixture was graduallytemperature-regulated to 240° C. with stirring. A temperature of about192° C. marked the onset of boiling. By-produced water at the onset ofboiling was continuously removed from the reaction via the waterseparator. The esterification generated about 90 ml (5.0 mol) of waterof reaction. The reaction time was about 7 hours.

The reaction was tracked by gas chromatography. The batch wasdiscontinued before the proportion of monoester had dropped below 2.0area %.

For aftertreatment, the reaction effluent from the esterification wastransferred into a 2 l flask which, following admixture of 2% by weightof activated carbon (CAP Super from Norit), was connected to a Claisenbridge with vacuum divider. An immersion tube with nitrogen terminus anda thermometer were fitted. Then, starting at 210° C. in vacuo (<40mbar), the bulk of the excess acid was distilled off. The batch wascooled down to 100° C. in a stream of nitrogen by injection of water.The batch was dried in vacuo (<40 mbar) for 20 min and then vented withnitrogen.

The 4 times molar excess of 10% NaOH solution was added at 80° C., andstirring was continued under nitrogen sparging for a further 15 min. Thebatch was then heated to 180° C. in vacuo and mixed with a further 5% byweight of water to keep the steam distilling going. Further water wasinjected to reduce the reaction temperature to 130° C. The reactionmixture was subsequently dried in vacuo in a temperature range of130-80° C. The ester was filtered through a Büchner funnel with filterpaper and precompacted filter cake of filter aid (D14 Perlite) by vacuumin a suction bottle. The filtrate was subjected to a GC analysis.

Product 12 (cf. Table 1) was synthesized according to the followingprotocol:

1.5 mol of isosorbide (from Cerestar), 3.8 mol of a defined C8/C10 fattyacid mixture (each from Sigma Aldrich) as per number 12 in Table 1 and0.020 mol of hypophosphorous acid (50% aqueous solution, from SigmaAldrich) were initially charged to an esterification apparatusconsisting of a 2 l multi-neck flask equipped with a stirrer, animmersion tube, a sampling stud, a thermometer and a water separatormounted with an intensive condenser.

The apparatus was flushed with 6 l of N₂/hour per hour via the immersiontube before the start of the reaction. The reaction itself took placewith nitrogen sparging. The reaction mixture was graduallytemperature-regulated to 240° C. with stirring. A temperature of about200° C. marked the onset of boiling. By-produced water at the onset ofboiling was continuously removed from the reaction via the waterseparator. The esterification generated about 53 ml (2.9 mol) of waterof reaction. The reaction time was about 2.5 hours.

The reaction was tracked by gas chromatography. The reaction wasdiscontinued before the proportion of monoester had dropped below 2.0area %.

For aftertreatment, the reaction effluent from the esterification wastransferred into a 2 l flask which, following admixture of 2% by weightof activated carbon (CAP Super from Norit), was connected to a Claisenbridge with vacuum divider. An immersion tube with nitrogen terminus anda thermometer were fitted. Then, starting at 210° C. in vacuo (<40mbar), the bulk of the excess acid was distilled off while the remainingacid was subsequently removed by stripping with nitrogen at 190 to 200°C. (in the course of about 2 hours). The reaction mass was subsequentlycooled down to <90° C. and the flask was vented with nitrogen. 2% byweight of Al₂O₃ was then added to the reaction mixture which was stirredfor 60 min at around 80° C. The ester was filtered through a Büchnerfunnel with filter paper and precompacted filter cake of filter aid (D14Perlite) via a suction bottle. The filtrate was subjected to a GCanalysis.

Product 13 (cf. Table 1) was synthesized according to the followingprotocol:

1.5 mol of isosorbide (from Cerestar), 6.0 mol of a defined C8/C10 fattyacid mixture (each from Sigma Aldrich) as per number 13 in Table 1 and0.011 mol of sulfuric acid (95-97% strength, from Sigma Aldrich) wereinitially charged to an esterification apparatus consisting of a 2 lmulti-neck flask equipped with a stirrer, an immersion tube, a samplingstud, a thermometer and a water separator mounted with an intensivecondenser (batch 13).

The apparatus was flushed with 6 l of N₂/hour per hour via the immersiontube before the start of the reaction. The reaction itself took placewith nitrogen sparging. The reaction mixture was graduallytemperature-regulated to 180° C. with stirring. By-produced water at theonset of boiling was continuously removed from the reaction via thewater separator. The esterification generated about 58 ml (3.2 mol) ofwater of reaction.

The reaction was tracked by gas chromatography. The batch was notdiscontinued when the proportion of monoester had dropped below 2.0 area%, and not even when the proportion of monoester had dropped to below1.0 area %.

The reaction time was about 15 hours. Thereafter, the reaction wasterminated and the proportion of high and low boilers was againdetermined (see Table 1).

For aftertreatment, the reaction effluent from the esterification wastransferred into a 2 l flask which, following admixture of 2% by weightof activated carbon (CAP Super from Norit), was connected to a Claisenbridge with vacuum divider. An immersion tube with nitrogen terminus anda thermometer were fitted. Then, starting at 210° C. in vacuo (<40mbar), the bulk of the excess acid was distilled off while the remainingacid was subsequently removed by stripping with nitrogen at 190 to 200°C. (in the course of about 2 hours). The reaction mass was subsequentlycooled down to <90° C. and the flask was vented with nitrogen.

The ester was filtered through a Büchner funnel with filter paper andprecompacted filter cake of filter aid (D14 Perlite) via a suctionbottle. The filtrate was subjected to a GC analysis.

Product 14 (cf. Table 1) was synthesized according to the followingprotocol:

1.5 mol of sorbitol (from Cerestar), 3.8 mol of a defined C8/C10 fattyacid mixture (each from Sigma Aldrich) as per number 14 in Table 1 and46.25 g of Amberlyst 46 (from Sigma Rohm & Haas) were initially chargedto an esterification apparatus consisting of a 2 l multi-neck flaskequipped with a stirrer, an immersion tube, a sampling stud, athermometer and a water separator mounted with an intensive condenser.

The apparatus was flushed with 6 l of N₂/hour per hour via the immersiontube before the start of the reaction. The reaction itself took placewith nitrogen sparging. The reaction mixture was graduallytemperature-regulated to 145° C. with stirring. By-produced water at theonset of boiling was continuously removed from the reaction via thewater separator. Esterification and ring closure generated about 110 ml(6.1 mol) of water of reaction.

The reaction was tracked by gas chromatography. The batch was notdiscontinued when the proportion of monoester had dropped below 2.0 area%, and not even when the proportion of monoester had dropped to below1.0 area %.

The reaction time was about 8 hours. The aim of this synthesis was togenerate a large proportion of high boilers.

For aftertreatment, the reaction effluent from the esterification wastransferred into a 2 l flask which, following admixture of 2% by weightof activated carbon (CAP Super from Norit), was connected to a Claisenbridge with vacuum divider. An immersion tube with nitrogen terminus anda thermometer were fitted. Then, starting at 210° C. in vacuo (<40mbar), the bulk of the excess acid was distilled off while the remainingacid was subsequently removed by stripping with nitrogen at 190 to 200°C. (in the course of about 2 hours). The reaction mass was subsequentlycooled down to <90° C. and the flask was vented with nitrogen.

The ester was filtered through a Büchner funnel with filter paper andprecompacted filter cake of filter aid (D14 Perlite) via a suctionbottle. The filtrate was subjected to a GC analysis.

Characterizing the Ester Mixture as Regards the C8/C10 Ratio (Analysis):

Procedure for Fatty Acid Analysis after Transesterification to theMethyl Ester

The C8/C10 ratio of the fatty acids in dianhydrohexitol di-fatty acidesters can be determined by transesterification to the methyl esters andsubsequent gas-chromatographic measurements.

The samples were worked up in accordance with Ph. Eur. 01/2008:20422corrected 6.8 Method C (fatty acid assay in polysorbate) and comparedwith the test mixtures described there. Sample preparation procedure wasas follows:

0.1 g of sample was admixed with 2.0 ml of NaOH solution (20 g of NaOH/lof anhydrous methanol) and refluxed for 30 minutes. Then, 2.0 ml ofmethanolic boron trifluoride solution (140 mg/ml) were added beforerefluxing for a further 30 minutes.

Following admixture of 4.0 ml of n-heptane the reaction solution wasrefluxed for a further 5 minutes and then cooled down to roomtemperature. The organic phase was extracted once with 10 ml ofsaturated sodium chloride solution and then a further three times with2.0 ml of Milli-Q water. The organic phase was dried over about 0.2 g ofanhydrous sodium sulfate. The upper clear phase was used for analysis.

GC analysis was performed with the parameters as follows:

capillary column: 30 m DB-WAX, 0.32 mm ID, 0.5 μm film

carrier gas: helium

column head pressure: 100 kPa

split: about 100 ml/min

oven temperature: 80° C.-10° C./min-220° C. (40 min)

injector: 250° C.

detector (FID): 250° C.

injection volume: 1.0 μl

The components in the sample chromatogram were identified using acomparative solution of the relevant fatty acid methyl esters. In thiscase, the methyl esters here are those of caproic acid, caprylic acid,capric acid, lauric acid and myristic acid. The signals in the samplechromatogram were subsequently standardized to 100 area %.

The mass ratio was computed using a computed response factor between theC8 and C10 fatty acid methyl ester and standardization of the twocomponents to 100%. This gives the C8/C10 ratio as standardized % bymass.

The standardized mass percent ratio was subsequently arithmeticallyconverted into a standardized mol % ratio.

The method described above was used to obtain ester mixtures whereinn-octanoic acid and n-decanoic acid were used as reactants in thefollowing molar ratios: 85:15, 75:25, 65:35, 58:42, 57:43, 50:50, 40:60,25:75.

The products obtained from the synthesis and also the pure isosorbide2,5-dioctanoate ester and the pure isosorbide 2,5-didecanoate ester wereeach analysed by the procedure described above to determine the fattyacid distribution. The results are summarized below in Table 1.

TABLE 1 Feed ratio and product composition of recited isosorbidediesters. C8/C10 ratio by GC C8/C10 C8/C10 after ratio by GC ratio by GCsaponi- after C8 pro- C10 pro- after fication sapon- portion portion ofLow High sapon- [standard- ification of feed feed boilers Diestersboilers ification ized % by [standard- No. [mol %] [mol %] [area %][area %] [area %] [area %] mass] ized mol %] — 100 0 0.20 98.74 1.0599.9/0.0  100.0/0.0  100.0/0.0   3 85 15 0.39 98.90 0.71 79.9/19.883.0/17.0 85.4/14.6  4 75 25 0.26 98.92 0.81 68.0/31.8 72.1/27.975.5/24.5  5 65 35 0.26 99.18 0.52 58.0/42.0 62.6/37.4 66.7/33.3  6 5842 0.23 99.08 0.69 48.3/51.5 53.2/46.8 57.6/42.4  7 57 43 0.18 98.671.04 47.9/51.8 52.8/47.2 57.2/42.8  8 50 50 0.26 99.33 0.40 42.8/56.947.6/52.4 52.0/48.0  9 40 60 0.38 99.28 0.34 32.9/66.9 37.3/62.741.5/58.5 10 25 75 0.29 99.56 0.14 19.9/79.6 23.2/76.8 26.5/73.5 — 0 1000.39 99.53 0.08  0.2/99.4  0.0/100  0.0/100.0 11 57 43 2.2 97.3 0.553.0/46.2 58.1/41.9 62.4/37.6 12 57 43 4.6 95.0 0.4 52.7/46.2 58.0/42.062.3/37.7 13 57 43 0.1 94.8 5.0 53.4/45.2 58.9/41.1 63.1/36.9 14 57 430.3 74.3 25.5 53.8/45.0 59.1/40.9 63.3/36.7

All samples were also measured for their Hazen colour number (APHA). Itwas found to be below 40 for the samples up to 12 inclusive. It was 160for sample 13 and 433 for sample 14. The values above 80 areundesirable, since they deliver significantly discoloured products.

Comparative Tests for Plastisol Application:

1. Production of Plastisol

The PVC plastisol produced was of the type which is used, for example,to fabricate topcoat films for floor coverings. The particulars in theplastisol recipes are each in weight fractions. The PVC used wasVestolit B 7021-Ultra. The comparative substances used were diisononylphthalate (DINP, VESTINOL 9 from Evonik Industries) and the isosorbidediester based on isononanoic acid (ISDIN-IS). The recipes of the polymercompositions are listed in Table 2.

TABLE 2 Recipe: Additive-Charge: 1 2 3* 4* 5* 6* 7* 8* 9 10 B 7021-Ultra100 100 100 100 100 100 100 100 100 100 DINP 50 ISDIN-IS 50 C8:C10 =85:15 50 C8:C10 = 75:25 50 C8:C10 = 65:35 50 C8:C10 = 58:42 50 C8:C10 =57:43 50 C8:C10 = 50:50 50 C8:C10 = 40:60 50 C8:C10 = 25:75 50 Drapex 393 3 3 3 3 3 3 3 3 3 Mark CZ 149 2 2 2 2 2 2 2 2 2 2 *polymer compositionaccording to the invention

The C8/C10 ratio used to synthesize the ester mixture is reported forsamples 3 to 10 in column 1 of Table 2. The values accordingly correlatewith columns 2 and 3 of Table 1. The resultant composition in the estermixture obtained can be seen in the last column of Table 1.

In addition to the 50 parts by weight of plasticizer, every recipefurther contains 3 parts by weight of an epoxidized soya bean oil asco-stabilizer (Drapex 39, from Galata), and also 2 parts by weight of aCa/Zn-based thermal stabilizer (Mark CZ 149, from Galata).

The plasticizers were conditioned to 25° C. prior to addition. Theconstituents were weighed into a PE beaker, first the liquid ones andthen the pulverulent ones. The mixture was hand mixed with a pastespatula until no unwetted powder remained. The mixing beaker was thenclamped into the clamping apparatus of a dissolver stirrer. Prior toimmersion of the stirrer into the mixture, the rotation rate was set to1800 revolutions per minute. Once the stirrer had been switched on,stirring was continued until the temperature on the digital display ofthe thermosensor reached 30.0° C. This ensured that homogenization ofthe plastisol was achieved with a defined energy input. The plastisolwas thereafter immediately conditioned at 25.0° C.

2. Measurement of Plastisol Viscosities

The viscosities of the PVC plastisols were measured using a Physica MCR101 instrument (from Anton-Paar) in the rotation mode and with themeasurement system “CC27”.

The plastisol was initially homogenized once more in the mixing vesselby stirring with a spatula, then filled into the measurement system andmeasured isothermally at 25° C. The following points were targetedduring the measurement:

1. A pre-shear of 100 s⁻¹ for a period of 60 s, during which no measuredvalues were recorded (to even out any thixotropic effects).

2. A downward shear-rate progression starting at 200 s⁻¹ and ending at0.1 s⁻¹, divided into a logarithmic series of 30 steps each of 5 secondsduration.

The measurements were as a rule (unless otherwise stated) carried outfollowing a 24 h storage/ripening period for the plastisols. Theplastisols were stored at 25° C. between the measurements.

Table 3 below shows the viscosity of each PVC paste at a shear rate of100 s⁻¹. Paste number correlates with the recipe number in Table 2.

TABLE 3 paste number 1 2 3 4 5 6 7 8 9 10 paste viscosity 5.73 10.8 6.326.60 6.64 6.68 6.77 6.84 6.99 7.35 after 24 h (100 s-1 )

Comparing the pastes, the pastes formed from the inventive polymercompositions (3, 4, 5, 6, 7, 8) have a significantly lower pasteviscosity than the paste comprising ISDIN-IS (paste number 2). Usingpurely ISDIN-IS (non-inventive polymer composition 2) it is virtuallyimpossible to produce a readily processable PVC paste, since its pasteviscosity is very high.

PVC pastes based on an inventive polymer composition versus a similarpaste based on an isosorbide ester of isononanoic acid have,irrespective of the shear rate, a lower shear viscosity and hence animproved processability.

3. Gelling Behaviour

The gelling behaviour of the pastes was studied in a Physica MCR 101 inoscillation mode using a plate-on-plate measurement system (PP25),operated with shear-stress control. An additional temperature-regulatinghood was attached to the equipment in order to homogenize heatdistribution and achieve a uniform sample temperature.

The settings for the parameters were as follows:

Mode: temperature gradient

-   -   starting temperature: 25° C.    -   final temperature: 180° C.    -   heating/cooling rate: 5° C./min    -   oscillation frequency: 4-0.1 Hz ramp logarithmic    -   angular frequency omega: 10 1/s    -   number of measurement points: 63    -   measurement-point duration: 0.5 min    -   automatic gap adjustment F: 0 N    -   constant measurement-point duration    -   gap width: 0.5 mm

Measurement Procedure:

A spatula was used to apply a drop of the paste to be measured, freefrom air bubbles, to the lower plate of the measurement system. Care wastaken here to ensure that some paste could exude uniformly out of themeasurement system (although not more than about 6 mm overall) after themeasurement system had been closed. The temperature-regulating hood wasthen positioned over the specimen and the measurement was started. Theso-called complex viscosity of the paste was determined as a function ofthe temperature. Since a certain temperature is attained within a timespan (determined by the heating rate of 5° C./min), information isobtained about the gelling rate of the measured system as well as aboutits gelling temperature. The onset of the gelling process wasdiscernible in a sudden marked rise in the complex viscosity. Theearlier the onset of this viscosity rise, the better the gellability ofthe system.

The measured curves obtained were used to determine the cross-overtemperature. This procedure computes the point of intersection for thetwo y-variables chosen. The procedure is used to find the end of thelinear viscoelastic region in an amplitude sweep (y: G′, G″; x: gamma)in order to find the crossing frequency in a frequency sweep (y: G′, G″;x: frequency) or to ascertain the gel time or cure temperature (y: G′,G″; x: time or temperature). The cross-over temperature documented herecorresponds to the temperature of the first intersection of G′ and G″.

The results are shown in Table 4. Paste number correlates with therecipe number in Table 2.

TABLE 4 paste number 1 2 3 4 5 6 7 8 9 10 cross-over 75.4 76.4 70.5 71.272.8 73.6 72.7 72.6 74.9 75.8 temperature ° C.

Gelling Behaviour:

Compared with the paste which contains ISDIN-IS (paste number 2), thepastes which contain an inventive polymer composition (paste numbers 3to 8) exhibit significantly faster gelling. The gelling of pastes 3 to 8is also faster than the gelling of pastes 9 and 10 and also of paste 1,which comprises the existing industry standard DINP.

4. Melting Points of Purely Ester Mixtures

Melting points were determined using Differential Scanning Calorimetry(DSC), in each case on the basis of the signal for the onset of melting.In the case of two or more melting points, the highest melting point wasreported, since the first crystallizations ensue below this temperature.

The results are shown in Table 5. Plasticizer number correlates with therecipe number in Table 2.

TABLE 5 plasticizer number 1 2 3 4 5 6 7 8 9 10 temperature ° C. n.d.n.d. 7 3 3 5 5 7.5 13 22 n.d. = not determinable

No melting point could be determined for plasticizer numbers 1 and 2.These substances merely exhibit a glass transition, since they areamorphous.

All melting points above 10° C. fail to satisfy the criteria for aplasticizer to be readily employable in large-scale industrialprocesses, since the products otherwise would have to be excessivelyheated at cold times of the year, which would lead to very high energycosts in order to ensure adequate flowability. Excessive heating couldalso induce premature gelling of the pastes even during the mixingoperation, combined with a pronounced tendency to thicken, and hencesignificantly compromised processability.

Isosorbide esters with exclusively C8-acid or C10-acid have acomparatively high melting point and are accordingly economicallyunviable for plastisol methods (this corresponds to about one third ofall commercial applications) for the abovementioned reasons. The C8/C10mixtures all without exception have lower melting points and areaccordingly significantly more suitable.

Avoidance of High Boilers

The formation of large proportions of high boilers leads to asignificantly comprised performance of the plasticizer, specifically asregards processability (gelling) and efficiency (Shore hardness). Toreduce the content level of high boilers in the product mixture, themethod of the present invention provides that the esterificationreaction be tracked by gas chromatography.

High boilers can form for example at high temperatures combined withlong reaction times or on using certain mineral acids, for examplesulfuric acid or sulfonic acids. This can lead to ring opening on thepart of the dianhydrohexitol, or the corresponding mono- or diester, toform the monoanhydrohexitol or the corresponding esters. The excess offatty acids can then lead to formation of di-, tri- and tetraesters ofmonoanhydrohexitol. The reaction is accordingly terminated as soon asthe proportion of monoesters drops below a certain value ingas-chromatographic measurements.

It was surprisingly found that the proportion of monoesters in thereaction mixture provides good control of the proportion of high boilersin the product mixture.

Avoidance of Low Boilers

The formation of low boilers leads even at low mass fractions to adeterioration in plasticizer performance, specifically its extraction inwater and its volatility. The monoesters are one example of such lowboilers.

As noted in connection with high boilers, long reaction times can leadto the formation of high boilers. A drastically reduced reaction time,however, leads to reduced conversions and hence to fatty acid monoestersof dianhydrohexitol which are low boilers. Temperature and reaction timetherefore have to be optimized so as to achieve the highest possibleconversion of dianhydrosorbitol and monoester while at the same timeavoiding the formation of high boilers to any significant extent. Thiswas achieved by terminating the reaction as soon as the proportion ofmonoesters had dropped below a certain value in gas-chromatographicmeasurements.

Characterizing the Ester Mixture as Regards Low and High Boiler Content(Analysis):

The content level of low and high boilers was determined by gaschromatography. High boilers have a higher retention time on an apolarcolumn than the C10,C10-ester. Low boilers have a lower retention timeon an apolar column than the C8,C8-ester. According to the presentinvention, the signals in the gas chromatogram are assigned using GC/MSanalyses. To record the gas-chromatographic spectra, for example, 0.1 gof sample was dissolved in 1.5 ml of acetone and transferred into a GCvial.

The gas-chromatographic analyses can in principle be carried out usingany commercially available GC instrument equipped with the suitableapolar column. An Agilent instrument of the 6890 N type was used for thepresent gas-chromatographic analyses. The temperature of the oven wasmaintained at 120° C. for 1.4 min, then raised to 350° C. at a heatingrate of 12.5 K/min and maintained at 350° C. for a further 17 min. Thegas-chromatographic spectra were recorded using an Agilent HP5 column,via an FID detector, with helium as carrier gas. Other commerciallyavailable GC instruments operated with the same operating parametersgave comparable results. In this case, too, the signals have to beassigned once via GC/MS measurements.

The retention time range of the dianhydrohexitol fatty acid esters isbetween 15 and 22 min in the example under consideration. The lowboilers are detected at between 6 and 15 min and the high boilers atbetween 22 and 32 minutes.

The area % proportions are determined using merely ester signals, i.e.low boilers and high boilers as per the above definition and the diestermixture itself; that is, solvent or carboxylic acid signals are notco-integrated.

Comparative Tests for Plastisol Application:

1. Production of Plastisol

The PVC plastisol produced was of the type which is used, for example,to fabricate topcoat films for floor coverings. The particulars in theplastisol recipes are each in weight fractions. The PVC used wasVestolit B 7021-Ultra. C8:C10 denotes the n-octanoic acid to n-decanoicacid ratio in which these reactants were used in the synthesis. Therecipes of the polymer compositions are listed in Table 6. Recipe numbercorrelates with the number in the first column of Table 1.

TABLE 6 Recipes for plastisol production recipe: Additive -- Charge: 7*11 12 13 14 B 7021 -- Ultra 100 100 100 100 100 C8:C10 = 57:43 50 C8:C10= 57:43 50 C8:C10 = 57:43 50 C8:C10 = 57:43 50 C8:C10 = 57:43 50 Drapex39 3 3 3 3 3 Mark CZ 149 2 2 2 2 2 *polymer composition comprising anester mixture obtained by a method according to the present invention

In addition to the 50 parts by weight of plasticizer, every recipefurther contains 3 parts by weight of an epoxidized soya bean oil asco-stabilizer (Drapex 39), and also 2 parts by weight of a Ca/Zn-basedthermal stabilizer (Mark CZ 149).

The ester mixtures were conditioned to 25° C. prior to addition. Theconstituents were weighed into a PE beaker, first the liquid ones andthen the pulverulent ones. The mixture was hand mixed with a pastespatula until no unwetted powder remained. The mixing beaker was thenclamped into the clamping apparatus of a dissolver stirrer. Prior toimmersion of the stirrer into the mixture, the rotation rate was set to1800 revolutions per minute. Once the stirrer had been switched on,stirring was continued until the temperature on the digital display ofthe thermosensor reached 30.0° C. This ensured that homogenization ofthe plastisol was achieved with a defined energy input. The plastisolwas thereafter immediately conditioned at 25.0° C.

2. Volatility

Plasticizer volatility was determined using an HB 43-S halogen dryerfrom Mettler Toledo. An empty clean aluminium dish was placed in theweighing pan prior to measurement. Thereafter, the aluminium dish wastared with a fibrous nonwoven web and about five grams of plasticizerwere pipetted onto the fibrous nonwoven web and weighed.

The heating module was closed to start the measurement and the samplewas heated at the maximum heating rate (pre-set) from room temperatureto 200° C. and every 30 seconds the loss of mass at that point due toevaporation was automatically determined by weighing. After 10 min themeasurement was automatically ended by the instrument.

A duplicate determination was carried out for every sample.

The results are shown in Table 7. Plasticizer number correlates with therecipe number in Table 6.

TABLE 7 Plasticizer number 7 11 12 13 14 loss of 3.50 3.71 4.55 2.692.71 mass [%]

The polymer composition comprising an ester mixture obtained by anon-inventive method (plasticizer No. 12) gives a significantly higherloss of mass than polymer compositions comprising an ester mixtureobtained by an inventive method (plasticizer numbers 7, 11, 13).

3. Water Resistance

Ageing resistance under various ambient conditions is a furtheressential quality criterion for PVC plasticizers. Especially thebehaviour with regard to water (water imbibition & leachability ofrecipe constituents) and with regard to elevated temperatures(evaporation of recipe constituents & thermal ageing) offers an insightinto ageing resistance.

If a plastic article imbibes water to a major degree, this changes notonly the materials properties thereof but also its visual appearance(e.g. haze). High water imbibition is accordingly undesirable ingeneral. Leachability is an additional criterion for setting thedurability of formulation constituents under service conditions. Thisholds particularly for stabilizers, plasticizers and/or constituentsthereof, since any reduction in the concentration of these recipeconstituents in the plastic article can not only worsen the materialsproperties but also drastically shorten the useful life.

Water resistance was determined using fully gelled 1 mm polymer films ofthe corresponding plastisols (gelling conditions in Mathis oven: 200°C./2 min). The test specimens used were roundels 3 cm in diameter cutout of the films. Before being lodged in water, the test specimens werestored in a desiccator containing a drier (KC drying beads from BASF SE)at 25° C. for 24 hours. The initial weight was determined with ananalytical balance to an accuracy of 0.1 mg. The test specimens werethen stored in a shaker bath (of the WNB 22 type with “CDP” Peltiercooling, from Memmert GmbH) filled with completely ion-free water at atemperature of 30° C. for 7 days under the water surface with sampleholders while being continuously agitated.

After lodgement, the roundels were removed from the water bath, driedoff and weighed (=weight after 7 days). The difference from the initialweight was used to compute the water imbibition. After being reweighed,the test specimens were again stored for 24 hours at 25° C. in adesiccator containing a drier (KC drying beads) and then once morereweighed (final reweighing=weight after drying). The difference fromthe initial weight before water lodgement was used to compute thepercentage loss of mass due to water lodgement (corresponds to loss byleaching).

The results are shown in Table 8. Test specimen number correlates withthe recipe number in Table 6.

TABLE 8 test specimen number 7 11 12 13 14 loss of −0.05 −0.55 −1.08−0.02 −0.19 mass [%]

The mass lost by test specimen 11 is slightly up compared with the masslost by test specimen 7, while that of test specimen 12 (having a highlow-boiler content) is significantly up.

Significantly increased losses of mass severely limit the utility ofplasticizers.

4. Plasticizing Effect

Its Shore hardness is a measure of the softness of a test specimen. Thefurther a standardized needle is able to penetrate into the testspecimen during a certain period of measurement, the lower the measuredvalue obtained. The plasticizer with the highest efficiency produces thelowest value of Shore hardness for the same amount of plasticizer. Sinceformulations/recipes are in practice frequently standardized/optimizedto a certain Shore hardness, accordingly, very efficient plasticizersmake it possible to save a certain proportion in the recipe, and thisrepresents a cost reduction for the processor.

To determine the Shore hardnesses, the pastes obtained as describedabove were poured into round brass moulds 42 mm in diameter (weightpoured into mould: 20.0 g). The pastes in the moulds were then gelled at200° C. in a circulating air drying cabinet for 30 min, removed aftercooling and stored for at least 24 hours in a conditioning cabinet (25°C.) before measurement. Disc thickness was about 12 mm.

The hardness measurements were carried out to DIN 53 505 using a Shore Ameter from Zwick-Roell, the measured value being read off after 3seconds in each case. Measurements were carried out at three differentplaces on each test specimen and averaged.

The results are shown in Table 9. Test specimen number correlates withthe recipe number in Tables 2 and/or 6.

TABLE 9 test specimen number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Shore A 8084 80 81 80 82 82 82 82 83 83 82 83 88

Compared with test specimen 2, which contains isosorbide esters based onisononanoic acid (ISDIN-IS) as plasticizer, test specimens 3-10 and11-13 exhibit a lower Shore A hardness, i.e. greater “softness”. Themethod of the present invention thus delivers ester mixtures that have abetter efficiency in PVC mixtures than ISDIN-IS has. Plasticizer canaccordingly be thereby saved, which leads to lower recipe costs. Recipe14, comprising an ester mixture obtained by a non-inventive method, hasa significantly higher Shore hardness.

Foams

The invention further claims the use in foams of an ester mixtureaccording to the invention.

Many PVC articles are typically made to include layers of foam in orderthat the weight of the products and thus also the costs may be reducedby virtue of the lower material requirements. Floorings, wall coveringsor artificial leathers are exemplary fields of use here. The user of afoamed product can benefit from superior structureborne sound insulationin the case of floor coverings for example.

The quality of foaming depends on many components within the formulationin that the type of PVC used and the plasticizer play an important partas well as the type and amount of foam former used. Plasticizers mustaccordingly deliver foamable compositions that are of low volatility,and allow faster processing at lower temperatures.

A foamable composition contains in general a polymer selected from thegroup consisting of polyvinyl chloride, polyvinylidene chloride,polyvinyl butyrate, polyalkyl methacrylate and copolymers, a foam formerand/or foam stabilizer and a plasticizer.

EXAMPLE F1 Production of Expandable/Foamable PVC Plastisols (withoutFiller and/or Pigment)

The advantages of a plastisol according to the present invention willnow be illustrated using a thermally expandable PVC plastisol thatcontains no filler and no pigment. The below plastisol according to thepresent invention is inter alia exemplary of thermally expandableplastisols used in the production of floor coverings. More particularly,the below plastisols according to the present invention are exemplary offoam layers used as back-side foams in PVC floorings of multilayeredconstruction. The formulations presented are couched in general terms,and can/have to be adapted by a person skilled in the art to thespecific processing and service requirements applicable in theparticular use sector.

TABLE 10 Composition of expandable PVC plastisols from Example F1. [Allparticulars in parts by mass] plastisol recipe (Example F1) 1** 7*Vinnolit MP 6852 100 100 VESTINOL ® 9 59 isosorbide ester (No. 7) 59Unifoam AZ Ultra 7043 3 3 zinc oxide 2 2 **comparative example*inventive example

The materials and substances used are more particularly elucidated inwhat follows:

Vinnolit MP 6852: microsuspension PVC (homopolymer) with K-value (as perDIN EN ISO 1628-2) of 68; from Vinnolit GmbH & Co KG.

VESTINOL® 9: diisononyl (ortho)phthalate (DINP), plasticizer; fromEvonik Industries AG. isosorbide ester: dianhydrohexitol fatty aciddiester with a composition as per compound No. 7 in Table 1.

Unifoam AZ Ultra 7043: azodicarbonamide, thermally activatable blowingagent; from Hebron S.A.

zinc oxide: ZnO, decomposition catalyst for thermal blowing agent,lowers the inherent decomposition temperature of the blowing agent, alsoacts as stabilizer,

“Zinkoxid Aktiv®”; from Lanxess AG. The zinc oxide was premixed with asufficient portion (1 phr) of the particular plasticizer used and thenadded.

Liquid and solid constituents of the formulation were weighed separatelyinto a suitable PE beaker for each. The mixture was hand stirred with apaste spatula until no unwetted powder was left. The plastisols weremixed using a VDKV30-3 Kreiss dissolver (from Niemann). The mixingbeaker was clamped into the clamping device of the dissolver stirrer. Amixer disc (toothed disc, finely toothed, Ø: 50 mm) was used tohomogenize the sample. For this, the dissolver speed was raisedcontinuously from 330 rpm to 2000 rpm, and stirring was continued untilthe temperature on the digital display of the thermosensor reached 30.0°C. (temperature increase due to friction energy/energy dissipation; seefor example N. P. Cheremisinoff: “An Introduction to Polymer Rheologyand Processing”; CRC Press; London; 1993). It was accordingly ensuredthat the plastisol was homogenized with a defined energy input.Thereafter, the plastisol was immediately conditioned at 25.0° C.

EXAMPLE F2 Production of Foam Foils and Determination ofExpansion/Foaming Behaviour at 200° C. of Thermally ExpandablePlastisols Obtained in Example F1

1. Production of Foam Foils and Determination of Expansion Rate

Foaming behaviour was determined using a thickness gauge suitable forflexible-PVC measurements (KXL047, from Mitutoyo) to an accuracy of 0.01mm. A Mathis Labcoater (type: LTE-TS, manufacturer: W. Mathis AG) wasused for foil production after adjustment of the roll blade to a bladegap of 1 mm. This blade gap was checked with a feeler gauge and adjustedif necessary. The plastisols were coated with the roll blade of theMathis Labcoater onto a release paper (Warran Release Paper, from SappiLtd.) stretched flat in a frame. To be able to compute percentagefoaming, first an incipiently gelled and unfoamed foil was produced at200° C./30 seconds' residence time. The thickness of this foil (=initialthickness) was in all cases between 0.74 and 0.77 mm at the stated bladegap. The thickness was measured at three different places on the foil.

Foamed foils (foams) were then likewise produced with/in the MathisLabcoater at 4 different oven residence times (60 s, 90 s, 120 s and 150s). After the foams had cooled down, the thicknesses were likewisemeasured at three different places. The mean thickness and the initialthickness were needed to compute the expansion. (Example: (foamthickness−initial thickness)/initial thickness*100%=expansion).

The results are shown in the following table (11):

TABLE 11 Expansion of polymer foams/foam foils produced from thermallyexpandable plastisols (as per Example F1) at different oven residencetimes in Mathis Labcoater (at 200° C.). plastisol recipe (as per ExampleF1) 1** 7* expansion after 60 s [%] 3 4 expansion after 90 s [%] 353 380expansion after 120 s [%] 495 515 expansion after 150 s [%] 511 522 **=comparative example *= inventive example

Compared with the current standard plasticizer DINP, significantlyhigher foam heights/expansion rates are achieved after a residence timeof 90, 120 and 150 seconds. The completeness of the decomposition of theblowing agent used and hence the progress of the expansion process isalso evident from the colour of the foam produced. The less theyellowness of the foam, the further the progress of the expansionprocess.

2. Determination of Yellowness Index

The YD 1925 yellowness index is a measure of yellow discolouration of asample specimen. This yellowness index is of interest in the assessmentof foam foils in two respects. First, it indicates the degree ofdecomposition of the blowing agent azodicarbonamide (=yellow in theundecomposed state) and, secondly, it is a measure of thermal stability(discolourations due to thermal stress). Colour measurement of the foamfoils was done using a Spectro Guide from Byk-Gardner. A (commerciallyavailable) white reference tile was used as background for the colourmeasurements. The following settings were used for the parameters:

illuminant: C/2°

number of measurements: 3

display: CIE L*a*b*

index measured: YD1925

The measurements themselves were carried out at 3 different places onthe samples (at a plastisol blade thickness of 200 μm for effect andflat foams). The values obtained from the 3 measurements were averaged.

The yellowness index determined for the polymer foams/foam foilsobtained in Example F2 is shown in the following Table (12).

TABLE 12 Y_(i) D1925 yellowness indices of polymer foams obtained inExample F1. plastisol recipe (as per Ex. F1) 1** 7* yellowness indexafter 60 s [%] 69 70 yellowness index after 90 s [%] 34 36 yellownessindex after 120 s [%] 25 24 yellowness index after 150 s [%] 25 24 **=comparative example *= inventive example

The yellowness indices of the foams are close together throughout theentire residence-time span. After 120 and 150 seconds, the yellownessindex is even at a lower level. The expansion rates and the yellownessindices demonstrate that fast processing is possible with the plastisolsof the present invention.

In addition to the presented example, foams containing fillers and/orpigments and also effect or flat foams are also for example obtainablewith the esters of the present invention. Effect foams refers to foamshaving a special texture on the surface. These foams are frequently alsoreferred to as “bouclé” foams after the appearance pattern known fromthe textile sector.

Useful fillers include, for example, calcium carbonates, silicates,talc, kaolin, mica, feldspar, wollastonite, sulphates, carbon black andmicrospheres. Fillers are frequently used at not more than 150 parts bymass, preferably at not more than 100 parts by mass, per 100 parts bymass of polymer.

The invention claimed is:
 1. An ester mixture, comprising a compound of formula (I):

wherein: R¹ and R² independently represent a C8-acyl group or a C10-acyl group, in which the C8-acyl group is derived from a C8-alkyl linear carboxylic acid, a C8-alkyl branched carboxylic acid, or a C8-alkene carboxylic acid that may be partially or completely epoxidized, and the C10-acyl group is derived from a C10-alkyl linear carboxylic acid, a C10-alkyl branched carboxylic acid, or a C10-alkene carboxylic acid that may be partially or completely epoxidized; and a proportion of C8-acyl groups relative to a total sum of the C8-acyl groups and C10-acyl groups in the ester mixture is from 50 mol % to 85 mol %.
 2. The ester mixture according to claim 1, wherein the proportion of the C8-acyl groups relative to the total sum of the C8-acyl groups and the C10-acyl groups in the ester mixture is from 50 mol % to 75 mol %.
 3. The ester mixture according claim 1, wherein the proportion of the C8-acyl groups relative to the total sum of the C8-acyl groups and the C10-acyl groups in the ester mixture is from 50 mol % to 65 mol %.
 4. The ester mixture according to claim 1, wherein a sum of the C8-acyl groups and the C10-acyl groups in the ester mixture has a proportion above 50 mol % relative to all acid chains in the ester mixture.
 5. The ester mixture according to claim 1, wherein R¹ is selected from the group consisting of a C8-acyl group derived from a C8-alkyl linear carboxylic acid, and a C10-acyl group derived from a C10-alkyl linear carboxylic acid.
 6. The ester mixture according to claim 1, wherein R² is selected from the group consisting of a C8-acyl group derived from a C8-alkyl linear carboxylic acid, and a C10-acyl group derived from a C10-alkyl linear carboxylic acid.
 7. The ester mixture according claim 1, comprising a mixture of the following three compounds:


8. A composition, comprising: the ester mixture of claim 1; and a high boiler, a low boiler, or a mixture thereof.
 9. The composition according to claim 8, wherein a proportion of high boilers is less than 15 area % based on ester signals in a gas-chromatographic analysis of the composition.
 10. The composition according to claim 8, wherein a proportion of low boilers is less than 4.5 area % based on the ester signals in a gas-chromatographic analysis of the composition.
 11. A polymer composition, comprising: the ester mixture of claim 1; and a polymer.
 12. A method of plasticizing a polymer, the method comprising combining the ester mixture of claim 1 with a polymer.
 13. A method for producing an ester mixture of claim 1, comprising: a) admixing n-octanoic acid and n-decanoic acid with a dianhydrohexitol; b) esterifying the n-octanoic acid and the n-decanoic acid with the dianhydrohexitol in the presence of a catalyst; and c) terminating the esterifying b) when a proportion of monoester of the dianhydrohexitol is below 2.0 area % based on a gas-chromatographic analysis.
 14. The method according to claim 13, wherein the catalyst is hypophosphorous acid.
 15. The method according to claim 13, wherein the n-octanoic acid and the n-decanoic acid are admixed in a molar ratio from 85:15 and 45:55.
 16. The method according to claim 13, wherein the n-octanoic acid and the n-decanoic acid are admixed in a molar ratio from 80:20 and 45:55.
 17. The ester mixture according to claim 1, wherein at least one R¹ or R² group contained in a compound of formula (I) in the ester mixture is defined as a C8-alkene carboxylic acid that is partially or completely epoxidized or as a C10-alkene carboxylic acid that is partially or completely epoxidized. 